Linear or Rotary Actuator Using Electromagnetic Driven Hammer as Prime Mover

ABSTRACT

We claim a hammer driven actuator that uses the fast-motion, low-force characteristics of an electro-magnetic or similar prime mover to develop kinetic energy that can be transformed via a friction interface to produce a higher-force, lower-speed linear or rotary actuator by using a hammering process to produce a series of individual steps. Such a system can be implemented using a voice-coil, electro-mechanical solenoid or similar prime mover. Where a typical actuator provides limited range of motion or low force, the range of motion of a linear or rotary impact driven motor can be configured to provide large displacements which are not limited by the characteristic dimensions of the prime mover.

This invention was made with government support under contract NNX12CE83P awarded by NASA. The government has certain rights in the invention.

CROSS REFERENCE TO RELATED APPLICATIONS

Not applicable

BACKGROUND OF THE INVENTION

Linear and rotary actuators are fundamental to virtually all industrial processing applications. Many advanced industrial and scientific processes involve extreme environments which are not ideal for traditional linear or rotary actuators. Extreme heat or cold, for example, may weaken rubber seals, jam gearboxes, or thicken lubricants. To date, very few actuators provide high force output without tight seals, gears, or lubrication. The proposed invention offers a compact, high force, and potentially non-grounded actuation system by use of an inertial hammering motion to significantly extend the displacement and force capabilities of a prime mover. The field of this invention is the field of actuator design. More specifically, the invention relates to the field of electro-mechanical motors used to produce actuators for industrial automation, flow control, valves, and motion control in general mechanical and industrial applications.

BRIEF DESCRIPTION OF PRIOR ART Construction Field—Pile Drivers

The pile driver is used in the field of civil construction using a similar mechanical impact action where the advancement of a shaft structure is dependent on an impact or hammer drive. Quoted from Wikipedia.org.

-   -   “A pile driver is a mechanical device used to drive piles         (poles) into soil to provide foundation support for buildings or         other structures . . . . One traditional type of pile driver         includes a heavy weight placed between guides so that it is able         to freely slide up and down in a single line. It is placed upon         a pile. The weight is raised, which may involve the use of         hydraulics, steam, diesel, or manual labour. When the weight         reaches its highest point it is then released and smashes on to         the pile in order to drive it into the ground” Quoted from         http://en.wikipedia.org/wiki/Pile driver

The construction field pile driver is not guided via a friction interface and does not make impacts in both directions.

Piezoelectric Inertial Slip or Stick Slip Motors

The field of piezoelectric actuators has presented a number of stick-slip and impact drive architectures. In the stick-slip (aka inertial-slip) architecture, the small amplitude high-bandwidth motion of piezoelectric element is used to provide “stepping mode” and/or “sliding mode” movement control of a “slider”. In stepping mode, the slider is advanced by the piezoelectric element—in a relatively slow movement, or “slow move”, where inertia prevents relative motion between the slider and a friction interface. In the “sliding mode” move, relative motion of the slider point of contact is initiated by executing a “fast move” with the piezoelectric element. During this fast move, the inertia of the slider prevents it from following the motion of the piezoelectric element and the acceleration of the point of contact mass overcomes the friction. By executing several slow move/fast move cycles, the small motion of the piezo-element can be used to generate relatively large displacements of the slider one “step” at a time. When finer control is needed, a lower amplitude slow move can be used to provide sub-step resolution.

Much like piezoelectric stick-slip motors, voice-coil actuators typically try to minimize the inertia associated with the moving elements in the actuator. This provides better response time and control over the limited working range of the actuator. While a number of actuation methods have been used to produce impact or hammer drives, to date, a voice-coil or inductive based system has not been presented in the literature or disclosed in patent filings [1, 2, 3] in the described configurations.

BRIEF SUMMARY OF THE INVENTION

A hammer driven actuator uses the high-speed, low-force characteristics of an electro-mechanical or pneumatic prime mover to develop kinetic energy that is transformed through an impact or impulse to an output to produce a higher force, lower speed, linear or rotary actuator with displacement and force characteristics that exceed the prime mover's capabilities. Where displacement and force capabilities of typical electro-mechanical and pneumatic actuators are limited by prime mover characteristics, the impact driven linear or rotary impact driven actuator can be configured to provide large displacements and higher forces not limited by the characteristic dimensions of the electro-mechanical prime mover.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 shows a voice coil actuator attached to an output shaft, along with a box frame structure around an impact collar.

FIG. 2 shows a rotary voice coil actuator attached to an output shaft that operates in a manner analogous to FIG. 1, but with a rotary output.

DETAILED DESCRIPTION OF THE INVENTION General Description of the Preferred Embodiment

A preferred embodiment of the present invention, as shown in FIG. 1, consists of a voice-coil prime mover that includes a winding (1) and a permanent magnet assembly (2). The permanent magnet assembly (2) is fixed to a box frame hammer structure (3). The magnet assembly (2) may have additional weight attached to increase its inertial mass. The winding (1) and an impact collar (4) are rigidly attached to an output shaft (7). The output shaft (7) is guided by a mounting flange (6) via a friction interface (5) which may also be considered a friction bushing. As current is applied to the winding (1), the permanent magnet assembly (2) and attached box frame hammer (3) are accelerated until the box frame hammer (3) strikes the impact collar (4). Kinetic energy of the permanent magnet assembly (2) and box frame hammer (3) is transferred to the impact collar (4). When the resulting impact force is sufficient to overcome the friction force provided by the friction interface (5), relative motion of the output shaft (7) is generated. In FIG. 1, the permanent magnet assembly (2) can be moved upward, driving the box frame structure (3) upward into the shaft collar (4), impacting the shaft collar with the lower face of the box frame hammer structure (3 a). The upward kinetic energy of the magnet assembly (2) and box frame hammer structure are transferred to the output shaft (7) via the impact collar (4). This sharp hammer impact creates motion by causing the output shaft (7) to slip through the friction interface (5). Motion in the reverse direction is accomplished by rapidly driving the hammer structure (3) from the top position to the bottom position, impacting the shaft collar with the upper surface of the box frame structure (3 b), causing downward motion.

An alternative embodiment is given by the rotary voice-coil prime mover impact drive (FIG. 2). As can be seen in the figure, this embodiment contains a winding (8) that can be used to generate an electromagnet, which is attached to an output shaft (11) with a free-spinning bearing or bushing (14), a set of permanent magnets (9 a and 9 b) attached to the output shaft (11) by rigid clamps (12 a and 12 b), a set of hammer pads (10 a and 10 b) attached to the winding (8), a set of impact plates (13 a and 13 b), and a friction interface (15). The winding (8) may have additional mass attached in order to generate higher impact energy. An electrical signal can be sent to the winding (8) in order to cause relative displacement with respect to the permanent magnets (9 a and 9 b). As the winding (8) moves it gains kinetic energy which is then transferred to one of the impact plates (13 a or 13 b) as it strikes the plate. This impact force is resisted by the static friction force developed by the friction interface (15). The permanent magnets and impact plates are mounted on a common assembly that is rigidly attached to the output shaft. When the impact force overcomes the static friction force provided by the friction interfaces, the output shaft (11) is displaced relative to the friction interface (15). The winding and hammer pads are incorporated into a second assembly which is mounted on a bearing (14) that allows them to rotate freely about the center shaft (11).

General Description of the Overall Technology

The invention can be applied to a family of relatively limited stroke electromagnetic actuators to be used as prime movers for a hammer drive to produce displacements in excess of the characteristic displacement found in the prime mover. Similarly, the characteristic force output of the prime mover can be amplified to produce significantly higher output forces through the use of a hammer driven operating configuration. An example of this conversion is as follows. A 0.6″ displacement, 16 pound capable voice-coil was set up in a hammer driven actuator embodiment. The voice coil was set up to drive the impact hammer. The resulting hammer driven actuator produced up to 100 pounds of force and 2 inches of displacement. The displacement can be increased based on additional guidance and bearings.

Additional embodiments use any type of relatively limited stroke rotary or linear actuator to produce the relatively high kinetic energy of the hammer structure to strike against the impact collar. Relatively limited linear and rotary actuators might include:

-   -   inductive solenoids,     -   moving coil voice-coils instead of moving magnet voice coils         described previously,     -   traction motors using Brushless or AC induction technology,     -   electrostatic actuators, and/or     -   other electromechanical limited stroke actuators that can         achieve high kinetic energy.

Additional embodiments include applications in which the friction clamp is part of the output device itself. For example, a gate valve has an innate friction required to close the valve. This actuator would be able to mount to the gate valve input without requiring a separate friction interface; the output load itself would act as the friction interface.

Additional embodiments use any type of pneumatic limited stroke rotary or linear actuator to produce the high kinetic energy hammer strike against the impact collar (or other impact feature). A pneumatic device with limited stroke could be used either with or without a biasing or return spring to generate the aforementioned impacts.

Additional embodiments include different kinetic impact absorption geometries. The description above, as well as FIG. 1, shows a box frame hammer structure. Other potential geometries include:

-   -   Simple collars attached to, or constructed as a part of, the         output shaft, such that vertical motion would impact a shaft         collar placed above or below the hammer mechanism (instead of an         enclosed box frame)     -   A version of any of the above types, but with one impact surface         being the mounting structure of the prime mover itself. For         example, a voice coil may bottom out in one direction, allowing         that to be one half of the impact interface. The other end may         be a shaft collar or similar.     -   A version of the above types, but with the impact geometries         internal to the prime mover instead of mounted externally.     -   A version of the above types with the magnet and coil in         reversed positions. 

We claim:
 1. An actuator comprised of: a. an inertial mass, b. an output shaft, c. one or more impact surfaces attached to the output shaft, d. one or more impact surfaces attached to the inertial mass, e. and a prime mover, itself comprised of an output part and a connection part, wherein the output part of the prime mover would traditionally be known as the “output” of the prime mover, and the connection part would traditionally be known as the “grounded” part.
 2. An actuator as described in claim 1 designed to have a linear output, and wherein the prime mover is a linear output actuator, and wherein this linear output prime mover is oriented in the system such that its output is approximately parallel to the output of the main actuator described in this patent
 3. An actuator as described in claim 1 designed to have a linear output, and wherein the prime mover is a rotary output actuator having a limited stroke, in which the rotary actuator is designed to impart kinetic energy to the output shaft (either directly or indirectly) by rotating into a kinetic impact transfer surface
 4. An actuator as described in claim 1 designed to have a rotary output, and wherein the prime mover is a rotary actuator, or wherein the prime mover is a linear actuator oriented in the system to provide a torque loading around the output shaft
 5. An actuator as described in claim 2, 3, or 4 wherein the output of the prime mover is the inertial part and wherein the connection part is securely attached to the output shaft.
 6. An actuator as described in claim 2, 3, or 4 wherein the output of the prime mover is securely attached to the output shaft and wherein the inertial part is the connection part.
 7. An actuator as described in claim 5 or 6, wherein the output shaft is connected via friction to a friction interface, which may be a dedicated friction interface clamp or may be an external device to be controlled by said actuator; as a non-limiting example, the actuator may be attached to a gate valve; since the gate valve itself has an innate friction component, the actuator will not need a separate friction interface
 8. An actuator as described in claim 7, wherein the impact surface attached to the output shaft and impact surface attached to the inertial mass are oriented such that the total output stroke of the prime mover is limited to below its characteristic output stroke by the geometrical arrangement of the impact surfaces, such that when the prime mover actuates to each extreme of motion, the stroke of the prime mover is limited by the impact surface on the output shaft colliding with the impact surface on the output part of the inertial mass
 9. An actuator as described in claim 8 that operates in either a linear or rotary fashion by using the prime mover to accelerate the inertial mass to a relatively high velocity, thus generating kinetic energy in the inertial mass; the actuator would then operate by allowing the moving inertial mass to contact the output shaft by means of colliding the impact surface on the inertial mass and impact surface on the output shaft, thus generating a large force in the system that is directly opposed by the friction interface described in claim 6; if this generated large force is sufficient to overcome the friction force generated by the friction interface described in claim 6, the output shaft will then move, causing gross motion of the entire actuator described in claim 4 or 5 (in other words, the entire actuator excluding the friction interface).
 10. An actuator as described in claim 9 wherein the prime mover is a voice coil actuator.
 11. An actuator as described in claim 9 wherein the prime mover is a solenoid actuator.
 12. An actuator as described in claim 9 wherein the prime mover is an electrostatic actuator.
 13. An actuator as described in claim 9 wherein the prime mover is an AC induction actuator.
 14. An actuator as described in claim 9 wherein the prime mover is a pneumatic piston device, either linear or rotary, with or without a spring bias or return mechanism.
 15. An actuator as described in claim 9 wherein the prime mover is a hydraulic actuator. REFERENCES [1] A. Morcos, “Latest Developments in voice coil actuators,” BEI, 1 Oct.
 2000. [Online]. Available: http://machinedesign.com/linear-motion/latest-developments-voice-coil-actuators. [Accessed 20 Aug. 2013]. [2] T. Morcos, “The Stright Attraction,” Motion Control, pp. 29-33,
 2000. [3] N. &. T. X. Wavre, “Voice-coil actuators in space,” Sixth European Space Mechanisms and Tribology Symposium, Proceedings of the conference held 4-6 Oct. 1995 in Zürich, Switzerland. Edited by W.R. Burke. ESA SP-374. European Space Agency, p. 227,
 1995. 